Yes. I got lucky and found someone selling a Wavetrac-equipped 3.46 and swapped that into my ZHP. It made an enormous difference. The car doesn't need one since it has pretty wide tires and not much power but it does make things considerably more fun when you want to drive like a dumb dumb. It also makes the car a lot more capable in the winter.Whoa. Does this just fit into the stock diff?? I'm reading up on it now and it seems really cool.
To echo bigglesworth you most likely don't want an M3 diff. You'll need the subframe as well as some other stuff and then you'll have a 3.64 final drive that will make you hate life on the highway. The 3.38 out of an automatic car is probably the perfect diff and, lucky you, you already have that ratio in yours (I think). Once you manual swap it you'll have a ton of fun.